To permit pumping of corrosive fluids such as high-temperature acids and the like, particularly in the semiconductor industry, positive displacement pumps have been developed which utilize a plastic bellows as a pumping member. Such bellows is constructed of Teflon and has a plurality of coils flexibly joined together to define an extendable and contractible sleeve, one end of which is closed, and the other end of which communicates with a source of pressurized air. This bellows is movably disposed within a pumping chamber in which the pumped fluid is alternately supplied and discharged. A drive piston is coupled between the bellows and is alternately and oppositely pressurized, such as with air, to cause alternative extension and contraction of the bellows to effect a pumping operation.
With this known pump, which is typically a double acting arrangement having a pair of bellows connected to opposite ends of and simultaneously driven by a common driver, it has been conventional to provide an interior support ring within each coil of the bellows to prevent inward collapse of the bellows during the pressurizing and pumping operation (that is, during the axial extension of the bellows). Such support ring typically comprises an elongate rod of spring material which is rolled to form a loop of a diameter slightly smaller than the interior diameter of the bellows coil. This loop is inserted into the bellows and then radially expanded so as to fill out and radially support the bellows coil. The ends of the split loop, which ends are flat, are disposed in abutting engagement with one another to hold the loop expanded and to form a substantially continuous ring for radially outwardly supporting the bellows coil. However, with this arrangement, it has been observed that the abutting ends of the support loop can become dislodged from one another. Thus, the loop tends to radially contract and the ends create edges which can effect undesired wear and possible puncturing of the thin plastic bellows.
Accordingly, this invention relates to an improved bellows-type pump which overcomes the aforementioned disadvantage. More specifically, the improved bellows-type pump of this invention incorporates an improved support ring which is positioned interiorly within the coil of the plastic bellows, which support ring is initially coiled to a diameter smaller than the normal bellows coil diameter. The free ends of the support ring have a telescopic relationship so that, when expanded to form a complete loop for supportive engagement within the bellows coil, the opposed free ends of the loop circumferentially engage one another and are positively held in telescopic engagement due to the circumferential hoop stress of the support ring. This thus greatly minimizes any tendency for the ends of the support ring to be sidewardly dislodged, and thus greatly minimizes any tendency for the bellows to become undesirable worn due to contact with the support ring ends.
Other objects and purposes of the invention will be apparent to persons familiar with pumps of this general type upon reading the following specification and inspecting the accompanying drawings.